Generally, contact lenses in wide use fall into three categories: (1) hard lenses formed from materials prepared by polymerization of acrylic esters, such as polymethyl methacrylate (PMMA), (2) rigid gas permeable (RGP) lenses formed from silicone acrylates and fluorosilicone methacrylates, and (3) gel, hydrogel or soft type lenses made of polymerized hydrophilic or hydrophobic monomers, such as 2-hydroxyethyl methacrylate (HEMA). The hard acrylic type contact lenses are characterized by low water vapor diffusion constants, resistance to the effects of light, oxygen and hydrolysis and absorb only minor amounts of aqueous fluids.
In the normal course of wearing contact lenses, tear film and debris consisting of proteinaceous, oily, sebaceous, and related organic matter have a tendency to deposit and build up on lens surfaces. Many factors influence deposit formation, including patient to patient variation, lens material, care regimen, and environment. In general, high water, ionic lens materials absorb more protein than low water or non-ionic lens materials. As part of the routine care regimen, contact lenses must be cleaned to remove these tear film deposits and debris. If these deposits are not properly removed, both the wettability and optical clarity of the lenses are substantially reduced causing discomfort for the wearer.
Conventionally, the cleaning of contact lenses is accomplished with one or both of two general classes of cleaners. Surfactant cleaners, generally known as "daily cleaners" because of their recommended daily use, are effective for the removal of most carbohydrate and lipid derived matter. However, they are not as effective for the removal of proteinaceous matter such as lysozyme. Typically, proteolytic enzymes derived from plant, animal, and microbial sources are used to remove the more tenacious proteinaceous deposits. These "enzyme" cleaners are typically recommended for weekly use and are commonly employed by dissolving enzyme tablets in suitable aqueous solutions.
Further, contact lenses must be disinfected to kill harmful microorganisms that may be present or grow on the lenses. A number of methods for disinfecting contact lenses have been used such as contacting the lenses with a solution containing an oxidative chemical (e.g. hydrogen peroxide) or an antimicrobial agent at ambient temperatures. Alternatively, disinfection may be accomplished by exposing the lenses to elevated temperatures for specified periods of time. This latter disinfection technique requires the use of a common electrical disinfecting apparatus.
A conventional process of cleaning and disinfecting contact lenses, particularly soft contact lenses, typically involves initial steps comprising the cleaning phase wherein the lenses are rubbed with a daily cleaner to remove debris and then soaked in an enzyme cleaning solution at ambient temperature conditions, i.e., soaking for a period of at least 15 minutes, to achieve effective removal of proteinaceous deposits. In this process, after the cleaning phase, it is necessary to subsequently disinfect the lenses.
Methods have been developed which can remove proteinaceous material from contact lenses while simultaneously disinfecting the lenses. For example, U.S. Pat. No. 4,614,549 discloses a single-step method of cleaning and disinfecting contact lenses in aqueous solutions of proteolytic enzymes at temperatures of between 60.degree. C. and 100.degree. C. Unfortunately, this method requires the use of an electrical disinfecting apparatus and elevated temperatures. Another example of a method for simultaneously cleaning and disinfecting contact lenses is described in U.S. Pat. No. Re. 32,672 which discloses a method wherein lenses are immersed in a solution containing peroxide and a peroxide active enzyme. However, this method requires an additional step for neutralization of the residual peroxide prior to inserting the lens into the eye.
In an effort to provide greater convenience, new regimens have been developed. For example, U.S. Pat. No. 5,096,607 issued Mar. 17, 1992 discloses a cleaning and disinfection system wherein lenses are simultaneous cleaned and disinfected by immersing the lens in a multi-purpose solution in the presence of an enzymatic tablet under certain conditions of osmolality. This system provides the benefit of a single "daily" cleaning and disinfection solution that may be simultaneously employed in combination with an enzymatic cleaner, thus reducing the number of steps required for effective lens cleaning and disinfection.
Although the latter patent represents a very significant improvement in cleaning lenses that is more convenient than previous systems, further convenience is sought. More specifically, it would be desirable to provide a cleaning system that employs only a single solution, without the general need for a supplemental enzymatic cleaning agent, which cleaning system is capable of providing cleaning comparable with systems which utilize enzymatic cleaners.